Autothermal hydrocarbon fuel reformers are known for the purpose of converting a raw hydrocarbon fuel to a hydrogen-enriched fuel which, with some additional cleanup, is suitable for use as a fuel gas for a fuel cell power plant. Typically, autothermal reformers are employed instead of conventional thermal steam reformers when heavier hydrocarbons are to be processed. Feed stocks such as gasoline or the like are better suited to be reformed by an autothermal reformer. The autothermal reformer is supplied with a mixture of air, steam and the raw fuel, and will catalytically convert this mixture to a hydrogen-rich processed fuel gas. In theory, most hydrocarbon feed stocks can be reformed to a hydrogen-enriched fuel cell reactant fuel by passing the air, steam and raw fuel over a catalyst bed in the reformer, wherein the following typical reaction takes place: EQU CH.sub.2 +2.55H.sub.2 O+0.35(O.sub.2 +4N.sub.2).fwdarw.CO.sub.2 +2.3 H.sub.2 +1.4N.sub.2 +1.25H.sub.2 O.
In operation, however, a number of factors can inhibit the ability of the reformer to perform its desired function. The reformer catalyst can be poisoned by constituents in the liquid raw fuel, particularly sulfur. In addition, carbon deposits can form in the vaporizer when the liquid raw fuel gas comes into contact with hot vaporizer surfaces before it vaporizes, thus fouling the vaporizer. Such carbon deposits would block vaporizer passages into the reformer, thus rendering the vaporizer unusable. The problem of carbon deposition in the vaporizer is particularly exacerbated when the raw fuel being processed is a liquid fuel, such as gasoline, fuel oil, kerosene, naphtha, diesel fuel, or the like.
In certain applications, such as in mobile fuel cell-powered applications, it would be desirable to be able to utilize liquid raw fuels such as gasoline, diesel fuel, or the like, which are commonly available at gas stations, as the process fuel which is to be reformed for use in a fuel cell power plant. In this way, a mobile vehicle such as an automobile, truck, bus, or the like could be electrically powered by electricity produced by an on board fuel cell power plant which employs such a liquid fuel as its hydrogen source. In order to obtain such a result, however, one would have to deal with, among other things, the problem of carbon deposition from the liquid fuel in the vaporizer.